In the technology of fermentation, bubbles generate in large quantities especially in fermentation that requires stirring and aeration, and this foaming has conventionally posed problems concerning operations. In case where the gas-phase part of the fermenter is filled with bubbles, not only the volume efficiency of the fermenter decreases but also there is a possibility that the bubbles might overflow the tank to wet the lines outside the tank, resulting in contamination. In order to inhibit such decreases in operation efficiency due to foaming, defoamers are added to fermentation systems. Since fermentation is always accompanied with stirring and aeration, the performances required of defoamers for fermentation include: foam-breaking properties which enable the defoamers to come to break the foam from the moment of addition thereof; foam-inhibiting properties which continuously inhibit foaming; and no inhibitory effect on the ferment organism. As such defoamers, defoamers of the type obtained by causing an alkylene oxide to add to both a fat or oil and a polyhydric alcohol as starting materials have been in general use because these defoamers have little inhibitory effect on the ferment organism and show excellent foam-breaking properties and foam-inhibiting properties.
Fermentation defoamers are diluted beforehand and are thereby added to fermentation systems as a dilution which is an aqueous solution or suspension having an even concentration. A general fermentation apparatus is configured so that when the bubbles generated in the fermenter reach a given height, this state is detected by a sensor and a defoamer dilution is supplied from a storage tank and added to the fermenter via an automatic dropping device. Since fermentation defoamers must show the effect thereof at 30 to 40° C., which are fermentation temperatures, many of the defoamers have a cloud point at temperatures lower by 10 to 20° C. than those temperatures. Such a defoamer is difficult to dissolve in or mingle with water at temperatures not lower than the cloud point, and a dilution thereof is hence prepared by cooling the system to or below the cloud point and stirring the cooled system. Consequently, dispersibility in water at the optimum temperature is required.
The defoamer dilution is sterilized by heating in order to prevent microorganisms from coming into the fermentation vessel, and is thereafter cooled to around the fermentation temperature and then added to the fermentation vessel. Because of this, the defoamer is exposed to temperatures not lower than the cloud point as a result of the heating in the sterilization step and has reduced solubility in water. This defoamer hence tends to precipitate in a lower-layer part or form oil droplets in an upper-layer to middle-layer part.
With respect to the fermentation defoamers which have formed a precipitate or oil droplets upon thermal sterilization, among conventional fermentation defoamers of the alkylene oxide adduct type, the defoamer dilutions have a reduced defoamer concentration in the liquid portion because the precipitate or oil droplets do not disappear even when the temperature thereof is lowered from the sterilization temperature to the fermentation temperature. Consequently, even when a defoamer dilution in this state is added to the fermenter, the inherent defoaming effect is not obtained. A step is therefore necessary in which the defoamer dilution is cooled again to or below the cloud point and stirred to thereby make the dilution return to the homogeneous dilution. The steps become complicated.
For example, the fermentation defoamer described in patent document 1 (Japanese Laid-Open Patent Application: JP-A-5-228308) is a defoamer obtained by causing alkylene oxides to add to a mixture of a fat or oil and a polyhydric alcohol. However, the amount of the ethylene oxide which has added to the starting materials is small as compared with the amount of the propylene oxide which has added to the starting materials and, hence, dilutions of this defoamer disadvantageously form oil droplets when heated. Meanwhile, the defoamer described in patent document 2 (International Publication WO 97/00942) is a blend system which is a blend of a defoamer of the type described above with a higher fatty acid, higher alcohol, or the like, and continuously shows the effect thereof over a long period without affecting the fermentation results. However, the higher fatty acid or higher alcohol, as a component of the blend, considerably decreases in solubility when dilutions of the defoamer are heated. This defoamer hence forms a precipitate or oil droplets, resulting in a decrease in defoaming effect.
In contrast, the defoamer described in patent document 3 (Japanese Laid-Open Patent Application: JP-A-6-54680) has the same basic structure as the defoamers of the type described above. However, the amount of the ethylene oxide which has added, relative to the amount of the propylene oxide which has added, is large. Because of this, this defoamer is less apt to form a precipitate or oil droplets during thermal sterilization, but is insufficient in defoaming effect. The defoamer described in patent document 4 (Japanese Laid-Open Patent Application: JP-A-2001-178446) is a defoamer obtained by causing 1 to 10 mol of propylene oxide to add to a mixture of a fat or oil and a polyhydric alcohol and then causing ethylene oxide and propylene oxide to randomly add thereto. This defoamer is less apt to form a precipitate or oil droplets during thermal sterilization, but shows low foam-breaking properties just after addition thereof. Consequently, some time is required for the effect thereof to be produced.
There has hence been no known fermentation defoamer which combines excellent dispersibility in water and a high defoaming effect.